1. Field of the Invention
Numerous deposit-forming substances are inherent in hydrocarbon fuels. These substances when used in internal combustion engines tend to form deposits on and around constricted areas of the engine contacted by the fuel. Typical areas commonly and sometimes seriously burdened by the formation of deposits include carburetor ports, the throttle body and venturies, engine intake valves, etc.
Deposits adversely affect the operation of the vehicle. For example, deposits on the carburetor throttle body and venturies increase the fuel to air ratio of the gas mixture to the combustion chamber thereby increasing the amount of unburned hydrocarbon and carbon monoxide discharged from the chamber. The high fuel-air ratio also reduces the gas mileage obtainable from the vehicle.
Deposits on the engine intake valves when they get sufficiently heavy, on the other hand, restrict the gas mixture flow into the combustion chamber. This restriction, starves the engine of air and fuel and results in a loss of power. Deposits on the valves also increase the probability of valve failure due to burning and improper valve seating. In addition, these deposits may break off and enter the combustion chamber possibly resulting in mechanical damage to the piston, piston rings, engine head, etc.
The formation of these deposits can be inhibited as well as removed by incorporating an active detergent into the fuel. These detergents function to cleanse these deposit-prone areas of the harmful deposits, thereby enhancing engine performance and longevity. There are numerous detergent-type gasoline additives currently available which, to varying degrees, perform these functions.
Two factors complicate the use of such detergent-type gasoline additives. First, with regard to automobile engines that require the use of nonleaded gasolines (to prevent disablement of catalytic converters used to reduce emissions), it has been found difficult to provide gasoline of high enough octane to prevent knocking and the concomitant damage which it causes. The chief problem lies in the area of the degree of octane requirement increase, herein called "ORI", which is caused by deposits formed by the commercial gasoline.
The basis of the ORI problem is as follows: each engine, when new, requires a certain minimum octane fuel in order to operate satisfactorily without pinging and/or knocking. As the engine is operated on any gasoline, this minimum octane increases and, in most cases, if the engine is operated on the same fuel for a prolonged period, will reach an equilibrium. This is apparently caused by an amount of deposits in the combustion chamber. Equilibrium is typically reached after 5,000 to 15,000 miles of automobile operation.
The octane requirement increase in particular engines used with commercial gasolines will vary at equilibrium from 5 to 6 octane units to as high as 12 or 15 units, depending upon the gasoline compositions, engine design and type of operation. The seriousness of the problem is thus apparent. A typical automobile with a research octane requirement of 85, when new, may after a few months of operation require 97 research octane gasoline for proper operation, and little unleaded gasoline of that octane is available. The ORI problem also exists in some degree with engines operated on leaded fuels. U.S. Pat. Nos. 3,144,311; 3,146,203; and 4,247,301 disclose lead-containing fuel compositions having reduced ORI properties.
The ORI problem is compounded by the fact that the most common method for increasing the octane rating of unleaded gasoline is to increase its aromatic content. This, however, eventually causes an even greater increase in the octane requirement. Moreover, some of presently used nitrogen-containing compounds used as deposit-control additives and their mineral oil or polymer carriers may also significantly contribute to ORI in engines using unleaded fuels.
It is, therefore, particularly desirable to provide deposit control additives which effectively control the deposits in intake systems of engines, without themselves eventually contributing to the problem.
In this regard, hydrocarbyl poly(oxyalkylene) aminocarbamates are commercially successful fuel additives which control combustion chamber deposits thus minimizing ORI.
The second complicating factor relates to the lubricating oil compatibility of the fuel additive. Fuel additives, due to their higher boiling point over gasoline itself, tend to accumulate on surfaces in the combustion chamber of the engine. This accumulation of the additive eventually finds its way into the lubricating oil in the crankcase of the engine via a "blow-by" process and/or via cylinder wall/piston ring "wipe down". In some cases, as much as 25%-30% of the non-volatile fuel components, i.e., including fuel additives, will eventually accumulate in the lubricating oil. Insofar as the recommended drain interval for some engines may be as much as 7,500 miles or more, such fuel additives can accumulate during this interval to substantial quantities in the lubricating oil. In the case where the fuel additive is not sufficiently lubricating oil compatible, the accumulation of such an oil-incompatible fuel additive may actually contribute to crankcase deposits as measured by a Sequence V-D test.
The incompatibility of certain fuel additives in lubricating oils, i.e., oils which contain other additives, arises in spite of the fact that some fuel additives are also known to be lubricating oil dispersants.
Several theories exist as to the cause of the lubricating oil incompatibility of certain fuel additives. Without being limited to any theory, it is possible that some of these fuel additives when found in the lubricating oil interfere with other additives contained in the lubricating oil and either counterbalance the effectiveness of these additives or actually cause dissolution of one or more of these additives including possibly the fuel additive itself. In either case, the incompatibility of the fuel additive with other additives in the lubricating oil demonstrates itself in less than desirable crankcase deposits as measured by Sequence V-D engine tests.
In another theory, it is possible that the accumulation of the fuel additive into the lubricating oil during the drain interval period surpasses its maximum solubility in the lubricating oil. In this theory, this excess amount of fuel additive is insoluble in the lubricating oil and is what causes increased crankcase deposits.
In still another theory, it is possible that the fuel additive will decompose in the lubricating oil during engine operation and the decomposition products are what cause increased crankcase deposits.
In any case, lubricating oil incompatible fuel additives are less than desirable insofar as their use during engine operation will result in increased deposits in the crankcase. This problem can be severe. For example, hydrocarbyl poly(oxyalkylene) aminocarbamate fuel additives, including hydrocarbyl poly(oxybutylene) aminocarbamate, are known to possess dispersant properties in lubricating oil. In this regard, it is recognized that the hydrocarbyl poly(oxybutylene) aminocarbamates are substantially more expensive than the hydrocarbyl poly(oxypropylene) aminocarbamates. However, because heretofore no known hydrocarbyl poly(oxypropylene) aminocarbamate was found to be sufficiently lubricating oil compatible, it was necessary to employ the more expensive hydrocarbyl poly(oxybutylene) aminocarbamates which are sufficiently lubricating oil compatible. Accordingly, it would be particularly advantageous to develop a hydrocarbyl poly(oxypropylene) aminocarbamate which is compatible in lubricating oil compositions.
The instant invention is directed to fuel compositions containing a novel class of hydrocarbyl poly(oxypropylene) aminocarbamates which as a fuel additive controls combustion chamber deposits thus minimizing ORI and in lubricating oil is compatible with the lubricating oil composition. The novel additives of this invention are alkylphenyl poly(oxypropylene) aminocarbamates having a molecular weight of about 600 to 6,000 wherein the alkyl group is substantially straight chain containing at least 15 carbon atoms.
2. Prior Art
Numerous references disclose hydrocarbyl poly(oxyalkylene) aminocarbamates as fuel additives. These include the following U.S. Pat. Nos.: 4,160,648; 4,243,798; 4,521,610; and 4,191,537; 4,270,930; 4,568,358; 4,197,409; 4,274,837; 4,236,020; 4,288,612.
Of particular relevance is U.S. Pat. No. 4,274,837 which discloses that hydrocarbyl poly(oxyalkylene) aminocarbamates containing certain poly(oxyalkylene) chains, i.e., oxypropylene, when used in fuels employed in combination with certain lubricating oils, produce crankcase varnish. This reference further discloses that lubricating oil compatible hydrocarbyl poly(oxypropylene) aminocarbamates are improved by employing the poly(oxypropylene) as a block copolymer having a terminus of 1 to 5 C.sub.9 to C.sub.30 oxyalkylene units.
U.S. Pat. No. 4,160,648 discloses an intake system deposit control additive for fuels which is a hydrocarbyl poly(oxyalkylene) aminocarbamate wherein the hydrocarbyl group is from 1 to 30 carbon atoms including alkyl or alkylphenyl groups. Specifically disclosed hydrocarbyl groups include tetrapropenylphenyl, olelyl and a mixture of C.sub.16, C.sub.18 and C.sub.20 alkyl groups. Likewise, U.S. Pat. No. 4,288,612 discloses deposit control additives for gasoline engines which are hydrocarbyl poly(oxyalkylene) aminocarbamates wherein the hydrocarbyl group contains from 1 to about 30 carbon atoms including alkylphenyl groups wherein the alkyl group is straight or branched chain of from 1 to about 24 carbon atoms. U.S. Pat. No. 4,568,358 discloses diesel fuel compositions containing an additive such as a hydrocarbyl poly(oxyalkylene) aminocarbamate. This reference discloses hydrocarbyl groups such as alkyl groups of 1 to 30 carbon atoms; aryl groups of 6 to 30 carbon atoms, alkaryl groups of 7 to 30 carbon atoms, etc.
U.S. Pat. No. 4,332,595 discloses hydrocarbyl poly(oxyalkylene) polyamines wherein the hydrocarbyl group is a hydrocarbyl radical of 8 to 18 carbon atoms derived from linear primary alcohols.
U.S. Pat. Nos. 4,233,168 and 4,329,240 among others disclose lubricating oil compositions containing a dispersant amount of a hydrocarbyl poly(oxyalkylene) aminocarbamate.
While these prior art references disclose fuel compositions containing C.sub.1 to C.sub.30 hydrocarbyl poly(oxyalkylene) aminocarbamates which include the poly(oxypropylene) polymers, none of these references disclose the unique hydrocarbyl group of this invention nor do any of these references suggest that use of this unique hydrocarbyl group would overcome the art recognized problem of lubricating oil incompatibility arising from using the prior art hydrocarbyl poly(oxypropylene) aminocarbamates.